The present invention relates to connectors for connecting wiring boards electrically to each other, and more particularly to connector structures for electrically connecting a multiplicity of electrodes which are formed densely on a substrate containing a multiplicity of semiconductor chips such as for constituting a part of a large-scale computer, the connector structures being suited for high-speed pulse transmission.
It has been desired to make an electronic apparatus such as a large-scale computer small in size and high in operating speed. Accordingly, it is strongly desired that a connector structure for electrically connecting substrates present in such an electronic apparatus, be small in size, have a multiplicity of electrodes, and have excellent high-speed pulse transmission characteristics.
In a mechanical connector structure which is used in a large-scale computer and employs a spring contact, problem include the difficulty in making the connector structure small in size maintaining and insertion/extraction force necessary for engaging and disengaging a substrate that is not excessive, particularly when the number of electrodes included therein is large. Further, in the mechanical connector structure, the electric capacitance between electrodes is as high as about 1 pF, and each electrode has an inductance of about 10 nH. Accordingly, the mechanical connector structure is unsuitable for high-speed pulse transmission. Meanwhile, a connector for connecting multi-pin electrodes to each other with a small insertion extraction force is proposed in an article entitled "Fabrication of Multiprobe Miniature Electrical Connector" (IBM Technical Disclosure Bulletin, Vol. 19, No. 1, 1976-6, pages 372 to 374). In this article, it is described that a connector structure which is small in size and requires small insertionextracton force can be formed by silicon lithography, and such connector structure is very useful for testing and packaging electronic circuits.
FIG. 1 shows a cross-section of a connector structure proposed in the above-mentioned article. In FIG. 1, reference numeral 1 designates a receptacle plate, 2 metal blocks having a low melting point, 3 electrode pins, 4 and 4' substrates each provided with electrode pins, and 5 octahedron-shaped through holes formed in the receptacle plate 1. The receptacle plate 1 is formed in such a manner that two silicon plates 1a and 1b each having truncated tetrahedron-shaped through holes are bonded to each other, and an insulating oxide film 7 is formed on the surface of the plate 1 and the inner wall of each through hole. A pair of facing electrode pins 3 are electrically connected to each other through the low melting point metal piece 2 loaded in the truncated octahedron-shaped through hole 5. When the metal block 2 is heated to temperatures higher than the melting point thereof, the substrates 4 and 4' can be inserted in and extracted from the connector structure with an insertion extraction force substantially equal to zero. Further, the substrates 4 and 4' can be fixed to the connector structure by solidifying the metal block 2 which was in a softened or molten state due to the heating.
For high-speed pulse transmission, however, the above connector structure causes such inconveniences as mentioned below, unless operated at an extremely low temperature. Referring again to FIG. 1, the receptacle plate 1 made of silicon is electrically conductive, unless kept at an extremely low-temperature, and hence the inner wall of each through hole 5 has to be coated with the insulating film 7 to electrically insulate an electrode made up of the low melting point metal block 2 and a pair of electrode pins 3 from the receptacle plate 1. In such a connector structure, the electric capacitance C between adjacent electrodes each made up of the members 2 and 3 is approximately expressed by the following equation: EQU C=(.epsilon.S)/(2t) (1)
where .epsilon. and t indicate the dielectric constant and the thickness of the insulating film 7 formed on the inner wall of each through hole 5, and S indicates an area for which the members 1 and 2 are opposed to each other. For example, when the insulating film 7 has a thickness of 2 .mu.m, the capacitance C lies in a range from 2 to 3 pF or may be greater than 3 pF which will bring about the problems of large reflection noise and a long delay time. Further, even when adjacent electrodes each made up of the members 2 and 3 are spaced apart from each other to some extent, a capacitor is formed between adjacent electrodes with a portion of the conductive receptacle plate 1 being interposed between adjacent electrodes, and thus the capacitance between adjacent electrodes does not decrease. Accordingly, there arised another problem that, crosstalk noise is increased. Further, since the reflection noise and the crosstalk noise are inversely proportional to the rising (or falling) time of a pulse signal to be transmitted, the transition speed of the pulse signal has to be limited to reduce each of the reflection noise and crosstalk noise to an allowable level.